The amount of N fixed by forage legumes and legume-grass systems was predicted by a combination of outputs from the CAPRI model and improved, country-specific N fixation coefficients. For grain legumes, the higher quality of available data made it possible to construct a detailed model based on N partitioning. Both approaches predicted quantities of N fixed that were broadly comparable with previously published estimates. Combining these figures with published crop production statistics allowed the production of detailed crop- and country-specific figures for N fixation by grain legumes that, for the first time, took into account the large differences in yields across Europe. The results also showed that while the amount of atmospheric N fixed into farming systems is likely to increase with increasing cultivation of many species of grain legumes, this is unlikely for beans and soya bean which apparently mine soil N reserves. Only minor adjustment to the Ndfa of soya bean, through management or breeding, is required to make it a net contributor to the N balance.
The results confirm that reliable estimates of agricultural N fixation in Europe require accurate crop production and yield statistics. Estimating N fixation would be greatly facilitated by changes to some of the information that is currently collected. This would result in more accurate figures for N fixed and N balance, which are crucial for reliable calculations of N losses such as nitrate leaching and emissions of the greenhouse gas N₂O. These are vital for refined predictions of the effects of strategic changes in the use of legumes in farming systems. Ultimately this will lead to the development of better policies to reduce the environmental impacts of European agriculture.

2014. Biological nitrogen fixation (BNF) by legume crops in Europe. Legume Hub. https://www.legumehub.eu